Fuel injection system for internal combustion engines



N. F. PRIBBLE Dec. 5, 1961 FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES Original Filed Sept. 24, 1956 RIO RIZ

INVENTOR. NOBLE F. PRIBBLE ATTORNEY United States 3,011,485 Patented Dec. 5, 1961 3,011,486 FUEL INJECTIGN SYSTEM FOR INTERNAL CGMBUSTION ENGINES Noble F. Pribble, Lutherville-Timonium, Md., assignor to The Bendix Corporation, a corporation of Delaware Original application Sept. 24, 1956, Ser. No. 611,654, now Patent No. 2,967,953, dated Jan. 10, 1961. Divided and this application Apr. 19, 1960, Ser. No. 23,241

Claims. (Cl. 123-119) This invention relates to a fuel injection system for internal combustion engines and more particularly to a fuel injection system incorporating transistorized multivibrator circuits of the monostable type wherein inductive control means are utilized.

This application is a division of my copending application Serial Number 611,654, filed September 24, 1956, now Patent 2,967,953, issued Jan. 10, 1961.

In certain uses of monostable multivibrators it is desirable to be able to accurately control the duration of the unstable state of the circuit and thus the duration of the output pulse thereof. In the past this has usually been done by the use of a combination of resistance and capacitance in which a capacitor is charged by the operation of the circuit in response to a triggering impulse and discharges through a resistor.

When power transistors are substituted for electron tubes, however, the low impedance of the transistors makes it diiiicult to utilize a resistance capacitance combination capable of providing an output pulse duration of any considerable value. For this reason only transistors of high impedance and low power handling capabilities can be used and an amplifier chain is required to amplify the multivibrator output to the level needed. Furthermore, the potentiometer necessary for varying pulse duration in the resistance capacitance control circuit has several drawbacks. It is expensive and subject to Wear which impairs its life and reliability.

It is an object of the present invention to provide a control for a monostable multivibrator which is adapted for use with the low impedances of power transistors.

It is a further object to provide such a control which is inexpensive, reliable and has a long life.

It is another object to provide a means for compensating for variations in amplitude of the multivibrator output due to variations in supply voltage level.

These and other objects and advantages of the invention are realized by a circuit in which an iron cored inductor is incorporated as a control element, and a separate inductor on the same core varies its saturation as a function of supply voltage level.

In the drawing:

FIG. 1 is a schematic diagram of a fuel injection system employing a circuit embodying the invention; and

FIG. 2 is a cross-sectional view of one form of control inductor.

By way of illustrating one use for a multivibrator of the type referred to and to disclose a complete system employing the invention, there is shown, in FIG. 1, a schematic representation of a fuel injection system for an internal combustion engine in which fuel is provided by means of a separate solenoid operated fuel injection valve for each cylinder of the engine. The energization of the solenoids is effected by the application thereto of the output pulses of the multivibrator which is triggered in synchronism with the rotation of the engine. The speed of the engine is controlled by the throttle setting which varies the duration of the pulses and which, in turn, varies the open time of the valves.

There is shown in FIG. 1 a shaft 1, which may be the distributor shaft of the engine, and is driven in accordance with engine rotation, The shaft 1 has mounted on it, for rotation therewith, a lobed cam 2 having a lobe for each engine cylinder. The cam is connected by a mechanical linkage 3 to one contact element of a single pole, single throw switch 4. This contact element is connected to a voltage reference plane shown as ground at 5.

The other contact element of the switch 4 is connected by way of a resistor R and a conductor 7 to a positive terminal 10 of a source of supply voltage. The said other terminal of switch 4 is also connected by way of a condenser C and a diode 12 to the base electrode of a transistor T The junction of capacitor C and diode 12 is connected to conductor 7 by a resistor R and the junction of diode 12 and the base electrode of transistor T is connected to conductor 7 by a resistor R The emitter electrode of transistor T is connected to the emitter electrode of a second transistor T and their junction is connected by a coil L to conductor 7. The coil has a movable iron core for varying its inductance. The core is indicated by the lines 13 and is connected by a mechanical linkage to a piston 15 driven by manifold vacuum. A second coil L is also wound about the core 13 and has one terminal connected by way of a resistor R to the conductor 7 and the other terminal connected to the voltage reference plane.

The collector electrode of transistor T is connected by way of a resistor R and that of transistor T by a resistor R to the voltage reference plane. The base electrode of T is connected through a resistor R to conductor 7 and through a resistor R to the Voltage reference plane.

The base electrode of T is connected through a resistor R to the collector electrode of T and through an additional resistor R to the base electrode of a third transistor T The emitter electrode of T transistor is connected by way of a resistor R to conductor 7 and by way of a resistor R to the voltage reference plane.

The collector electrode of T is connected by way of a resistor R and a conductor 23 to a wiping contact element 16 carried by and insulated from an arm 17 mounted on the shaft 1 for rotation therewith. The element 16 makes sequential wiping contact with a plurality of contact segments 18, of which one is provided for each cylinder, only two being shown. Each segment 18 is connected to one terminal of a respective solenoid 19 having an armature 20. The armature is a valve stem having a valve element 21 formed on its lower end. The element 21 seats in a seat 22 formed in the intake manifold of the engine close to the fuel intake valve of a respective cylinder. The remaining terminal of each solenoid 19 is connected to the voltage reference plane.

FIG. 2 illustrates a manner in which the coils L and L may be wound about the core 13. The coils are housed in a container 24.

In the operation of the circuit described above, the cam 2 closes the switch 4 and opens it once while the contact element 16 is wiping each segment 18. Closing of the switch causes the undriven contact of the switch to be placed at the potential of the ground reference plane, while opening the switch causes this contact to assome the voltage of the terminal 10. The result is a square Waveform as indicated at 25. This waveform is difierentiated by the combination of R and C and the negative-going spikes of the resulting waveform are passed by the low impedance of the diode 12 and applied to the base electrode of the transistor T In the multivibrator composed of T and T the transistor T is normally conducting. In this state there will be a drop of about 1.5 volts across the DC. resistance of the inductor L There will be a drop of .7 volt from the emitter of T to its collector. The drop across the resistor R is such that the base of T is biased to a positive potential with respect to its emitter and T will thus be cut oil.

When the switch '4 is closed the negative spike applied to the base electrode of T will cause T to conduct, which will increase the drop across the coil L This will reduce the conduction of T applying as a result a negative voltage to the base of T thus increasing the conduction of T This regenerative action will ter minate in the cut off of T T will remain cut oif until the current build up through the coil L is complete. When the emitter of T is again more positive than the base the reverse action will take place and T will conduct again. The time constant of this action is determined by theinductance of L and the resistance of R The inductance of L is varied by varying the position of the iron core 13.

The output of the multivibrator is applied through the resistor R to the base electrode of transistor T It is amplified in a conventional manner and applied by way of resistors R conductor 23, contact element 16, and contact segment 18 to thecoil 19.

The function of the coil L is to compensate for changes in the amplitude of the pulses in the output of the multivibrator due to changes in the voltage of the supply source. When this source is the battery of an automobile, for example, the voltage issubject to variation and tends to be low when starting and thus to provide a pulse of reduced amplitude. The reducedamplitude results in the injection valves being opened more slowly and an increase in pulse duration is needed to compensate for this effect. The coilL increases the saturation of the core when the supply voltage increases and this results in a reduction in the duration of the pulse. Conversely areduction in supply voltage decreases the saturation of the core and increases the duration of the pulse. This action is desirable, for example, when starting.

The use of the inductive control means described above makes it possible to use low impedance power type transistors for the multivibrator and to thus effect a reduction in the number of transistors needed for the whole circuit. The circuit illustrated utilizes three power transistors, Whereas with a resistance capacitance type of control circuit power transistors with their low impedances could not be used in the multivibrator and a total of five transistors would be required to provide the desired pulse output.

The component values shown on the drawing are provided solely for the purpose of illustrating typical satisan inductive element in said input circuit; means for continuously varying the inductance of said inductive element in accordance with a running function of the engine; means for varying the time duration of said pulses as a function of voltage changes in the power source; and, means actuated by said pulses for supplying fuel to the engine.

2. A fuel injection system as set forth in claim 1 in which the inductive element comprises a coil serially connected between the multivibrator input circuit and said power source, and in which the means for varying the inductance of said coil comprises: a movable core of magnetizable material; and means responsive to variations in the engine parameters for moving said core with respect to said coil.

3. A fuel injection system as set forth in claim 2 in which the means responsive to variations in engine parameters for moving said core comprises means responsive to variations in the intake vacuum of the engine.

4. A fuel injection system as set forth in claim 2 in which the means for varying the time duration of said pulses as a function of voltage changes in the power source includes asecond coil connected directly across the power source wound about said core.

5. A. fuel injection system as set forth in claim 1 in which the means for varying the time duration of said pulses as a function of voltage changes in the power source comprises: a movable core of magnetizable material extending into said inductive element; and, a coil connected directly across the power source wound about said core.

2.807.244 harclay Sept. 4. 1957 

